Examples of such valves can be found, for instance, in U.S. Pat. No. 4,673,393, U.S. Pat. No. 5,176,652 and US-A-2005/017,479.
A difficulty arises with the use of such a series of seals, however, in that in order to have good sealing characteristics they also tend to create a significant resistance to movement of an insert therein, which can substantially impair the operability of the insert by making it too hard to slide within the sheath. This can in some instances lead to damage of the insert, for example by kinking. This risk is particularly acute for inserts which are by necessity very flexible or of a small diameter.
In order to mitigate the above disadvantages, it is also known to use a haemostatic valve which can be opened and closed under the clinician's control. This has the advantage that an element can be inserted into the sheath and moved therealong with relative ease while the controllable haemostatic valve is in an open configuration. Once the insert is in place the valve can be tightened to seal. Such tightening is also advantageous during the procedure of insertion of the device into the sheath assembly. In practice, it is often necessary for such a solution also to include a valve which self-seals, such as one or more of the disk-shaped valves mentioned above to secure sealing during handling.
Such selectively openable and closable valve elements typically have an elongate valve member of tubular form which can be closed by twisting or by application of pressure laterally on the valve element by means of one or more movable closing plates.
U.S. Pat. No. 4,673,393, U.S. Pat. No. 5,176,652 and U.S. Pat. No. 6,981,996 disclose valve assemblies which include substantially planar valve elements of disc-shape with a number of slits therein. An insert, such as a pusher, dilator or other elongate element, can pass through the slit or slits and into the sheath of the deployment of the device. When such inserts are removed, the slits close in order to close the valve element.
There are a number of compromises with such valve elements. When an insert is passed through the valve to open the slits, the seal is no longer fluid tight, with the result that there can be leakage through the valve element. This problem can be mitigated by designing a valve element with an increased closure pressure, whereby the edges of the slit or slits push tightly against the insert so as to close around this to reduce leakage paths. However, increasing closure pressure increases the effective friction between any item inserted within the valve and the valve itself, which can make it harder to slide any insert through the valve. Such additional friction can also cause damage to any insert held therewithin and potentially cause damage to the valve itself. It will be appreciated that if such damage occurs in the middle of a medical procedure this can be highly disadvantageous, at worst resulting in an abortive procedure.
As explained above, attempts have been made to try to resolve the problem with such valves by providing a plurality of valves in series, with the slit or slits of each valve element being rotated relative to one another so as to provide a more effective seal. However, even though this might improve the sealing characteristics of the valve, it does not satisfactorily deal with the problem of increased pressure on or friction against the insert held therewithin.
US-A-2005/0,171,479 discloses a different type of valve element which is formed of an elongate tubular member which can be twisted so as to fold into a closed position at its centre. The material forming the valve element is sufficiently flexible that it can wrap itself around an insert held within the valve, thereby to provide the required seal. This type of valve has the advantage that when the valve element is opened, that is when it is in an untwisted state, it provides no or substantially no friction on an insert held therewithin. Of course, in practice it is necessary to provide additional sealing/valve elements. It is, for example, known to add disc-shaped seals of the type described above. In US-2005/0171479, for example, there are provided three disc-shaped seals in addition to the twistable cylindrical seal.
Another twistable seal is disclosed in US-2004/078586
An additional problem with the twistable seals disclosed in US-2005/0171479 and US-2004/0178586 is that the sealing efficiency of these seals is determined by the depth of the seal in the longitudinal direction of the valve, in practice the depth of the seal which comes into contact with the outer walls of the insert. This can be seen for example in FIG. 24 of US-A-2005/0171479 and in FIG. 2 of US-A-2004/0178586, in which only a small portion of the twistable valve element contacts the insert, thus providing a relatively narrow seal. A narrower seal provides less sealing effect and often also requires the provision of additional seals, such as the disc-shaped seals used in the device of US-A-2005/0171479.
Therefore, these twistable seal elements do not mitigate all of the disadvantages of haemostatic seals.
Another valve element for use in such deployment devices and also for endoluminal medical procedures includes a flexible valve element provided with two facing leaflets which are able to contact one another when the valve is closed so as to provide a seal. Particularly, one end of the valve element keeps the leaflets open, for example by provision of a support element holding to the two leaflets apart. At the other, free end, the leaflets can be made to contact one another when the valve is in a closed configuration, for example by sealing the side edges of the leaflets together. FIG. 1 shows a cross sectional view of an example of such a two-leaflet valve, in which an insert is located within the valve, causing the two leaflets to open.
A problem with this type of valve, as can be seen in FIG. 1, is that the valve element is unable to close well around the insert, leaving large apertures allowing leakage of fluid through the valve leaflets.